Catheters are inserted to various locations within a patient for a wide variety of purposes and medical procedures. For example only, one type of catheter is used in percutaneous catheter intervention (PCI) for the treatment of a vascular constriction termed a stenosis. In this instance, the catheter has a distally mounted balloon that can be placed, in a deflated condition, within the stenosis, and then inflated to dilate the narrowed lumen of the blood vessel. Such balloon dilation therapy is generally named percutaneous transluminal angioplasty (PTA). The designation PTCA, for percutaneous transluminal coronary angioplasty, is used when the treatment is more specifically employed in vessels of the heart. PTCA is used to open coronary arteries that have been occluded by a build-up of cholesterol, fats or atherosclerotic plaque. The balloon at the distal end of the catheter is inflated, causing the site of the stenosis to widen.
The dilation of the occlusion, however, can form flaps, fissures and dissections, which may result in reclosure of the dilated vessel or even perforations in the vessel wall. Implantation of a stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel or provide a patch repair for a perforated vessel wall until corrective surgery can be performed. A stent is typically a cylindrically shaped device formed from wire(s) or a tube and is intended to act as a permanent prosthesis. Stents may include therapeutic coatings or deliver therapeutic drugs to further treat the vessel and prevent reclosure of the vessel. A stent is deployed in a body lumen from a radially compressed configuration into a radially expanded configuration that allows it to contact and support a body lumen. A stent can be implanted during an angioplasty procedure by using a balloon catheter bearing a compressed stent that has been loaded onto the balloon. The stent radially expands as the balloon is inflated, forcing the stent into contact with the body lumen, thereby forming a supporting relationship with the lumen walls. Alternatively, self-expanding stents may be deployed with a sheath-based delivery catheter. Deployment is effected after the stent has been introduced percutaneously, transported transluminally and positioned at a desired location by the delivery catheter. In addition to angioplasty and stenting procedures, other therapeutic procedures require use of a delivery catheter, such as drug delivery, filters, occlusion devices, diagnostic devices and radiation treatment.
Typically, the placement of such therapeutic delivery catheters involves the use of a guide wire, which may be inserted into the patient's vasculature through the skin, and advanced to the location of the treatment site. The delivery catheter, which has a lumen adapted to receive the guide wire, then is advanced over the guide wire. Alternatively, the guide wire and the delivery catheter may be advanced together, with the guide wire protruding from the distal end of the delivery catheter. In either case, the guide wire serves to guide the delivery catheter to the location to be treated.
To treat small diameter vessels remote from the entry point into the patient, a guide catheter is used to span the distance. For example, in PTCA or stent delivery, a guide catheter 10 is typically inserted into a large artery 12 near the patient's groin, and then advanced toward the heart 14 to the entry opening, or ostium, of the diseased coronary artery as illustrated in FIG. 1A. The guide catheter 10 provides a tubular conduit through which catheters and guide wires, designated generally as 16, can be passed from outside the patient to the vessel being treated.
There are three general types of catheters: “over-the-wire” (OTW) catheters, “rapid exchange” (RX) or single operator catheters and “fixed wire” (FW) or “a balloon on a wire” catheters. An over-the-wire catheter comprises a guide wire lumen that extends the entire length of the catheter. The guide wire is disposed entirely within the catheter guide wire lumen except for the distal and proximal portions of the guide wire, which extend beyond the distal and proximal ends of the catheter respectively. An OTW catheter typically has a “co-axial” catheter construction, as shown in FIGS. 2A and 3A, wherein two hollow tubes are nested together such that the lumen 22 of the inner tube can slidably receive guide wires, such as guide wire 24, and the annular luminal space 26 formed between the inner and outer tubes is used for inflation/deflation, fluid. An alternative “multilumen” OTW catheter construction has an elongate shaft made from a single extruded tube 18 having two lumens 22′ and 26′ formed side-by-side, as shown in FIGS. 2B and 3B. OTW catheters that contain both multilumen segments and coaxial segments are also known.
Over-the-wire catheters have many advantages traceable to the presence of a full-length guide wire lumen such as good stiffness and pushability for readily advancing the catheter through the tortuous vasculature and across tight stenoses. The full-length guide wire lumen permits removal and replacement of a guide wire in an indwelling catheter, as may be required to alter the shape of the guide wire tip. It is also sometimes desirable to exchange one guide wire for another guide wire having a different stiffness. For example, a relatively soft, or flexible guide wire may prove to be suitable for guiding a PTCA catheter through a particularly tortuous anatomy, whereas following up with a stent-delivery catheter through the same vasculature region may require a guide wire that is relatively stiffer. The full-length guide wire lumen is also available for transporting radiocontrast dye to the stenosed artery, for making pressure measurements, for infusing drugs and for other therapies.
Over-the-wire catheters do suffer some shortcomings, however. For example, it often becomes necessary, in the performance of a PCI, to exchange one indwelling catheter for another catheter. In order to maintain a guide wire in position while withdrawing the catheter, the guide wire must be gripped at its proximal end to prevent it from being pulled out of the blood vessel with the catheter. For example, a PTCA catheter, which may typically be on the order of 135 centimeters long, is longer than the proximal portion of the standard guide wire that protrudes out of patient. Therefore, exchanging an over-the-wire PTCA catheter requires an exchange guide wire of about 300 centimeters long, whereas a standard guide wire is about 165 centimeters long.
In one type of over-the-wire catheter exchange, the standard length guide wire first is removed from the lumen of the indwelling catheter. Then, a longer exchange guide wire is passed through the catheter to replace the original wire. Next, while holding the exchange guide wire by its proximal end to control its position in the patient, the catheter is withdrawn proximally from the blood vessel over the exchange guide wire. After the first catheter has been removed, the next OTW catheter is threaded onto the proximal end of the exchange guide wire and is advanced along the exchange guide wire, through the guiding catheter, and into the patient's blood vessels until the distal end of the catheter is at the desired location. The exchange guide wire may be left in place or it may be exchanged for a shorter, conventional-length guide wire. In an alternative type of catheter exchange procedure, the length of the initial guide wire may be extended by way of a guide wire extension apparatus. Regardless of which exchange process is used, the very long exchange guide wire is awkward to handle, thus requiring at least two operators to perform the procedure.
Catheter designs have been developed in an attempt to eliminate the need for guide wire extensions or exchange guide wires. One such catheter design is the rapid exchange (RX) type catheter. Catheters of this type are formed so that the guide wire is located outside of the catheter except for a short guide wire lumen that extends within only a comparatively short distal segment of the catheter. The rapid exchange catheter's proximal exit port for the guide wire is typically located about 5 cm (2.0 in) to 100 cm (11.8 in) proximal to the catheter's distal end. In use, the guide wire is placed initially in the patient's vascular system. The distal segment of the RX catheter then is threaded onto the wire. The catheter can be advanced alongside the guide wire with its distal segment being attached to and guided along the guide wire. The RX catheter can be removed and exchanged for another RX catheter without the use of a very long exchange guide wire and without requiring withdrawal of the initially placed guide wire.
Although an RX catheter system may avoid the requirement for using a very long exchange wire, it presents several difficulties. First, without a full-length guide wire lumen, the proximal shaft of an RX catheter lacks an OTW catheter's coaxial interrelationship with the guide wire, which provides optimal transmission of force to push the distal end of the catheter through tight stenoses and/or tortuous blood vessels. FIGS. 2A and 3A illustrate guide catheter 10, a shaft segment of OTW catheter 18 extending there through, and guide wire 24 disposed within guide wire lumen 22 in the common construction of coaxial tubes. The nested tubes result in an inner guide wire lumen 22 and an annular inflation lumen 26 formed between the tubes. The coaxial interrelationship with guide wire 24 provides an optimal transmission of force along the catheter length. In FIGS. 2B and 3B, inflation lumen 26′ extends parallel to guide wire lumen 22′ in a side-by-side arrangement. Although guide wire lumen 22′ and guide wire 24′ are located off-center in catheter 18′, guide wire 24′ is confined within catheter 18′ throughout its length. Even if catheter 18′ begins to buckle slightly when the distal tip of the catheter is being forced through a tight stenosis, there is very little misalignment with guide wire 24′, such that most of the push force is transmitted to the distal tip. Therefore, despite their disadvantages during catheter exchange procedures, OTW catheters remain popular in the United States, due in part to the coaxial alignment between the catheter shaft and the guide wire, and the resulting excellent pushability of the device.
While improvements to RX catheters have incorporated stiff, metal proximal shafts and axial overlap between the shaft and the guide wire lumen to overcome the deficiencies discussed above, such RX catheters still are not optimal. FIGS. 4 and 5 depict prior art RX catheter 30 incorporating such a reinforced shaft 32, disposed over guide wire 34 within guide catheter 36. However, even with continuous column support of reinforced shaft 32, the non-aligned or offset arrangement of guide wire 34 and shaft 32 of catheter 30 can cause shaft buckling within the guiding catheter, as illustrated generally at 38 in FIG. 4, especially when the distal tip of the catheter is being forced through a tight stenosis. Such a non-coaxial misalignment causes displacement of push forces and an associated resistance to catheter advancement, especially in the region of proximal guide wire port 40.
A second difficulty associated with RX catheters is that it is not possible to exchange guide wires in an indwelling RX catheter, as can be done advantageously with OTW catheters. A guide wire can be withdrawn, sometimes unintentionally, from the proximal guide wire port, thus derailing an indwelling RX catheter. However, neither the first guide wire, nor a replacement guide wire, can be directed back into the catheter's proximal guide wire port, which is hidden remotely in the guiding catheter within the patient. FIG. 6 illustrates the problem of blindly steering the tip of guide wire 42 within guiding catheter 44 in an attempt to find and engage proximal guide wire port 46 of RX catheter 48.
A third difficulty associated with RX catheters is that, if the guide wire lumen is so short that the proximal guide wire port exits from the distal end of the guiding catheter, then the guide wire will be exposed. Such an RX device presents a risk of what is called the “cheese cutter effect,” which is damage to the delicate inner surface of a curved artery from straightening tension applied to the exposed guide wire during push-pull maneuvers to advance the catheter. The short-lumen RX device also presents an increased risk of guide wire entanglement in those procedures where multiple guide wires are used, because the guide wires are exposed within the blood vessel. Furthermore, the exposed, unprotected portion of the guide wire can become kinked or tangled within the patient's vessel, adding complications to the procedure.
A fourth difficulty associated with RX catheters is encountered at the proximal end of the catheter system. There, the RX catheter and the guide wire extend from the guiding catheter side-by-side, making it awkward to seal the system against blood loss during manipulation of the components. The sealing, or “anti-backbleed” function is typically accomplished with a “Tuohy-Borst” fitting that has a manually adjustable gasket with a round center hole that does not conform well to the side-by-side arrangement of a catheter shaft and guide wire. A final difficulty associated with RX catheters is that the lack of a full-length guide wire lumen deprives the clinician of an additional lumen that may be used for other purposes, such as pressure measurement, injection of contrast dye distal to the stenosis, or infusing a drug.
An over-the-wire catheter designed to eliminate the need for guide wire extensions or exchange wires is disclosed in U.S. Pat. No. 4,988,356 (Crittenden et al.). This over-the-wire/short wire (OTW/SW) catheter includes a catheter shaft having a cut that extends longitudinally between the proximal end and the distal end of the catheter and that extends radially from the catheter shaft outer surface to the guide wire lumen. A guide member slidably coupled to the catheter shaft functions to open the cut such that the guide wire may extend transversely into or out of the cut at any location along its length. By moving the guide member, the effective over-the-wire length of the OTW/SW catheter is adjustable.
When using the OTW/SW catheter, the guide wire is maneuvered through the patient's vascular system such that the distal end of the guide wire is positioned across the treatment site. With the guide member positioned near the distal end of the catheter, the proximal end of the guide wire is threaded into the guide wire lumen opening at the distal end of the catheter and through the guide member such that the proximal end of the guide wire protrudes out the proximal end of the guide member. By securing the guide member and the proximal end of the guide wire in a fixed position, the catheter may then be transported over the guide wire by advancing the catheter toward the guide member. In doing so, the catheter advances through the guide member such that the guide wire lumen envelops the guide wire as the catheter is advanced into the patient's vasculature. In a PTCA embodiment, the OTW/SW catheter may be advanced over the guide wire in this manner until the distal end of the catheter having the dilatation balloon is positioned within the stenosis and essentially the entire length of the guide wire is encompassed within the guide wire lumen.
Furthermore, the indwelling OTW/SW catheter may be exchanged with another catheter by reversing the operation described above. To this end, the indwelling catheter may be removed by withdrawing the proximal end of the catheter from the patient while holding the proximal end of the guide wire and the guide member in a fixed position. When the catheter has been withdrawn to the point where the distal end of the cut has reached the guide member, the distal portion of the catheter over the guide wire is of a sufficiently short length that the catheter may be drawn over the proximal end of the guide wire without releasing control of the guide wire or disturbing its position within the patient. After the catheter has been removed, another OTW/SW catheter may be threaded onto the guide wire and advanced over the guide wire in the same manner described above with regard to the OTW/SW catheter. The OTW/SW catheter not only permits catheter exchange without the use of the very long exchange guide wire and without requiring withdrawal of the initially placed guide wire, but it also overcomes many of the other difficulties discussed in association with RX catheters.
Despite these advantages, original OTW/SW catheters in accordance with the '356 patent had difficulties related to movement of the guide wire through the guide member. As disclosed in the '356 patent, the use of a hypodermic tubing member to direct a guide wire into and out of the guide wire lumen was found to be effective while the guide wire was stationary within the guide member, and while the catheter was moved therethrough. However, if the guide wire were to be withdrawn through the guide member, the hypodermic tubing member would often scrape pieces of a lubricious coating from the guide wire. The resulting shavings, designated generally as 50 in FIG. 7, would become jammed in the annular space between the guide wire 52 and the hypodermic tubing member 54, preventing further movement of the guide wire.
In a more significant problem with the original OTW/SW catheter, it could fail to adequately contain the guide wire within the guide wire lumen during normal operation. In particular, as the catheter was advanced over the guide wire, the catheter could bend or buckle such that the guide wire could protrude from the catheter shaft. If the guide wire protruded from the catheter shaft, it could subsequently become pinched, and the distal end of the guide wire could be pulled out of or pushed beyond the treatment site, thus complicating the procedure and requiring repositioning within the patient's vasculature. Bending or buckling of a OTW/SW catheter could also occur proximal to the guide member, where the guide wire is absent from the guide wire lumen. Furthermore, the transition between the proximal shaft containing the longitudinal cut and the distal part of the catheter is also a potential kink location. It is among the general objects of the invention to provide an improved device that overcomes the foregoing difficulties.